Lindsay, I know how hard it is to postpone something like Thanksgiving - but - I would let everyone know how sick I was so that they could decide whether or not to come and expose themselves to your crud. Maybe they will decide not to come!
That would be wonderful!!! However, they will probably come since plans are already made. I'd just try my best and let everyone know that you are sick and you will do what you can. If I couldn't go any more, I'd just crawl upstairs and go to bed for awhile and let everyone else proceed with fixing the meal. I'm so sorry you are sick! I got sick once the day before Christmas, but it was just my mom and daughter and family, so they just took over and did everything for me.